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(#) Assertions with Side Effects

!!! WARNING: Assertions with Side Effects
   This is a warning.

Id
:   `AssertionSideEffect`
Summary
:   Assertions with Side Effects
Severity
:   Warning
Category
:   Performance
Platform
:   Any
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   7.2.0 (May 2022)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/AssertDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AssertDetectorTest.kt)

Assertion conditions can have side effects. This is risky because the
behavior depends on whether assertions are on or off. This is usually
not intentional, and can lead to bugs where the production version
differs from the version tested during development.

Generally, you'll want to perform the operation with the side effect
before the assertion, and then assert that the result was what you
expected.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test.kt:5:Warning: Assertion condition has a side effect: setOf(42)
[AssertionSideEffect]
  assert(42 != f.setOf(42)) // WARN 1
               -----------
src/test.kt:6:Warning: Assertion condition has a side effect: f.of =
2024 [AssertionSideEffect]
  assert(2024 != (f.of = 2024)) // WARN 2
                  -----------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here are the relevant source files:

`src/test.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
import test.pkg.Foo

fun test() {
  val f = Foo()
  assert(42 != f.setOf(42)) // WARN 1
  assert(2024 != (f.of = 2024)) // WARN 2
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`src/test/pkg/Foo.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;
public class Foo {
    private int OF = 0;
    public int getOf() {
        return OF;
    }
    public int setOf(int v) {
        int prev = OF;
        OF = v;
        return prev;
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/AssertDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `AssertDetector.testSetOf_JavaSyntheticPropertySetter`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("AssertionSideEffect")
  fun method() {
     assert(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("AssertionSideEffect")
  void method() {
     assert(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection AssertionSideEffect
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="AssertionSideEffect" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'AssertionSideEffect'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore AssertionSideEffect ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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